Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A grease is provided which has an improved inflow property of the grease
into a lubrication unit and has a long life when used for bearings even
under a high temperature environment.
A grease composition comprising a base oil and a thickener, characterized
in that the base oil contains an ester synthetic oil, the content of the
ester synthetic oil is not less than 20% by mass of the total mass of the
base oil and the thickener contains a diurea compound represented by the
Formula (I):
R1--NHCONH--R2--NHCONH--R3, (I)
wherein R2 is a C6-15 divalent aromatic hydrocarbon group,
R1 and R3 are the same or different, and represent cyclohexyl
or C8-22 linear or branched alkyl, and the molar ratio of cyclohexyl
to the total of cyclohexyl and C8-22 linear or branched alkyl is 60
to 95%.

Claims:

1. A grease composition comprising a base oil and a thickener in the
amount of 10.0 wt % to 18.0 wt % based on the total weight of the grease
composition, characterized in that the base oil contains an ester
synthetic oil and oils other than the ester synthetic oil, the ester
synthetic oil is selected from the group consisting of complex ester
oils, the complex ester oils are synthesized from polyalcohols with
monovalent fatty acids and polyvalent base acids, the content of the
ester synthetic oil is not less than 20% by mass of total base oil, the
oils other than the ester synthetic oil is selected from the group
consisting of mineral oils, synthetic hydrocarbon oils, ether synthetic
oils, and combinations thereof, and the thickener contains a diurea
compound represented by the Formula (I):
R1--NHCONH--R2--NHCONH--R3, (I) wherein R2 is a
diphenylmethylene group, R1 and R3 are the same or different,
and represent cyclohexyl or C8-22 linear or branched alkyl and the
molar ratio of cyclohexyl to the total of cyclohexyl and C8-22
linear or branched alkyl is 70 to 90%.

2. The grease composition according to claim 1, wherein the polyalcohol
is pentaerythritol.

3. The grease composition according to claim 1, which is for bearings.

4. The grease composition according to claim 1, wherein the bearings are
rolling bearings for automobile electrical equipment or auxiliaries.

6. A bearing in which the grease composition according to claim 1 is
filled.

7. The grease composition according to claim 1, wherein the amount of the
thickener is about 14 wt %.

8. The grease composition according to claim 1, wherein the grease
composition is configured to have more than 500 hours of the bearing life
measured by the outer race rotating test and more than 500 hours of the
bearing life measured by the bearing lubrication life test.

Description:

TECHNICAL FIELD

[0001] This application is a continuation of U.S. application Ser. No.
12/593,111, now allowed, filed Sep. 25, 2009, which is the U.S. National
Phase of International Application No. PCT/JP2007/058800, filed Apr. 24,
2007, which designated the U.S. and claims priority to Japan Application
No. 2007-079734, filed Mar. 26, 2007 the entire contents of each of which
are hereby incorporated by reference.

[0002] The present invention relates to a grease composition and a
bearing, particularly to a grease composition suitably used for rolling
bearings for automobile electrical equipment or auxiliaries and to
rolling bearings for automobile electrical equipment or auxiliaries in
which the grease composition is filled.

BACKGROUND ART

[0003] A long lubrication life is required for a grease which lubricates a
portion such as rolling bearings for automobile electrical equipment or
auxiliaries, which is heated to extremely high temperatures and subjected
to extremely high speed movements. In order to provide a long lubrication
life, the properties of the grease to easily flow into the lubrication
unit, as well as heat-resistant property, are required. Such an inflow
property of the grease is particularly strongly required when outer race
rotation type bearings are used for the bearings, since it is more
difficult for the grease to flow into the lubrication unit, for example
due to the action of centrifugal force in the outer race rotation type
bearings. On the other hand, when the inflow property is too high, the
grease is soft and leaks from the bearings, and therefore the lubrication
life becomes short. Thus, a grease which has a good balance between
heat-resistant property and inflow property is demanded.

[0004] Examples of outer race rotating bearings for automobile electrical
equipment or auxiliaries include bearings used for electromagnetic
clutch, intermediate pulley, idler pulley, tension pulley and the like
used for automobile air conditioners. On the other hand, examples of
inner race rotating bearings include bearings used for alternators and
the like.

[0005] The grease which has a long life when used for outer ring rotation
type bearings may be used not only for the outer ring type bearings but
also for inner race rotation type bearings since, as described above, the
grease has a good balance between heat-resistant property and inflow
property.

[0006] Diurea greases which employ mainly a synthetic hydrocarbon oil or
phenyl ether synthetic oil as a base oil are used as the grease used for
rolling bearings for automobile electrical equipment or auxiliaries. In
many cases, an aromatic diurea grease is used among diurea greases since
it has an excellent high-temperature resistance. However, the lives of
this sort of greases are not nearly satisfactory when used for outer race
rotation type bearing because of insufficient inflow property of the
greases into the lubrication unit.

[0007] In the meantime, as an example of improving the inflow property by
a thickener, Patent Document 1 describes a grease composition in which
the diurea compound represented by the following general formula is
employed as a thickener in a base oil containing an ether synthetic oil
in an amount more than 50% by mass of the base oil:

R1--NHCONH--R2--NHCONH--R3,

wherein R2 represents C6-15 divalent aromatic hydrocarbon
group, R1 and R3, the same or different, represent cyclohexyl,
C7-12 cyclohexyl derivative groups or C8-20 alkyl; and the
ratio of the number of moles of cyclohexyl and derivative groups thereof
to the total number of moles of cyclohexyl, C7-12 cyclohexyl
derivative groups and C8-20 alkyl is 50 to 100%

[0008] However, this grease composition lacks in compatibility between the
base oil and the thickener, lacks in inflow property, and the life of the
bearing is not satisfactory.

[0009] Patent Document 1 JP 2979274B

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a grease
composition and a bearing.

[0011] Another object of the present invention is to provide a grease
which has an improved inflow property into a lubrication unit and has a
long life when used for bearings even under a high temperature
environment.

Means for Solving the Problems

[0012] The present invention provides the following grease composition and
bearings.

[0013] 1. A grease composition comprising a base oil and a
thickener, characterized in that the base oil contains an ester synthetic
oil, the content of the ester synthetic oil is not less than 20% by mass
of the total base oil and the thickener contains a diurea compound
represented by the Formula (I):

[0013] R1--NHCONH--R2--NHCONH--R3, (I)

[0014] wherein R2 is a C6-15 divalent aromatic hydrocarbon
group, R1 and R3 are the same or different, and represent
cyclohexyl or C8-22 linear or branched alkyl and the molar ratio of
cyclohexyl to the total of cyclohexyl and C8-22 linear or branched
alkyl is 60 to 95%.

[0015] 2. The grease composition according to the
above item 1, wherein the ester synthetic oil is an ester synthetic oil
which has three or more ester groups in the molecule.

[0020] 7. A bearing in
which the grease composition according to any one of the above items 1 to
6 is filled.

Effect of the Invention

[0021] The grease composition of the present invention has an improved
inflow property into the lubrication unit, which makes the bearing life
longer even under high temperature environments. Thus, it is an excellent
grease for bearings and exerts excellent effects as a grease for
bearings, particularly as a grease for rolling bearings for automobile
electrical equipment or auxiliaries and more particularly as a grease for
bearings used for outer race rotating of rolling bearings for automobile
electrical equipment or auxiliaries.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0022] As described above, inflow property of the grease into the
lubrication unit is required to obtain a long service life, and on the
other hand, when the inflow property is too high, the grease is soft and
leaks from the bearings, and therefore the life of the lubrication unit
becomes short. Thus, it is important that a grease has a good balance
between heat-resistant property and inflow property.

[0023] The grease of the present invention is characterized in that the
grease has a balance between heat-resistant property and inflow property
by controlling inflow property together with securing heat-resistant
property by increasing the ratio of cyclohexyl group in the
above-described diurea compound while improving the inflow property of
the grease by employing an ester synthetic oil which is compatible with
the thickener because the oil has a polarity.

[0024] Examples of thickeners generally used for a grease composition
include metallic soap thickeners containing Li, Na or the like; and
non-soap thickeners such as benton, silica gel, diurea compounds and
fluorinated thickeners represented by polytetrafluoroethylene. Metallic
soap thickeners, benton and silica gel, however, are not acceptable with
respect to the heat resistant property, that is, a bearing lubrication
life under a high temperature. Though the fluorinated thickener is
acceptable with respect to the heat-resistant property, the price of the
thickener is too high and lacks general versatility.

[0025] Therefore, the grease composition of the present invention is
characterized by employing a particular diurea thickener represented by
the general formula I.

[0026] In the general formula I, the molar ratio of cyclohexyl group to
the total of cyclohexyl group and C8-22 linear or branched alkyl
groups represented by R1 and R3 is 60 to 95%, more preferably
70 to 90%.

[0027] When the ratio is less than 60%, the grease is soft and leaks from
the bearings, and therefore the life of the bearings becomes short. When
the ratio is more than 95%, the grease becomes hard, and the inflow
property of the grease becomes worse, and therefore the life of the
bearings becomes short.

[0028] Examples of the base oils which are employed in the grease
composition of the present invention include ester synthetic oils.
Examples of the ester synthetic oils include diester oils represented by
di-2-ethylhexyl adipate (DOA), di-2-ethylhexylsebacate (DOS), di-isodecyl
adipate (DIDA) and the like; aromatic ester oils represented by
trimellitic acid ester oils and the like; and polyol ester oils
represented by trimethylolpropane ester oils, pentaerythritol ester oils
and the like.

[0030] The ratio of ester synthetic oil to the total base oil is
preferably not less than 20% by mass, more preferably not less than 50%
by mass, most preferably 100% by mass. In order to sufficiently obtain
the heat-resistant property and inflow property of the grease, not less
than 20% by mass of ester synthetic oil is preferably contained. This is
because ester synthetic oils facilitate the inflow property of the grease
into the lubrication unit, since the ester synthetic oils have a high
polarity and a high affinity for the thickener.

[0031] The base oil used for the grease of the present invention may
contain base oils other than the ester synthetic oils. Examples of the
other base oils include mineral oils and synthetic oils. Examples of the
synthetic oils include diester oils; synthetic hydrocarbon oils
represented by poly-α-olefin; ether synthetic oils represented by
alkyldiphenyl ether; polyglycol synthetic oils represented by
polypropylene glycol; silicone synthetic oils; and fluorinated synthetic
oils.

[0033] A base grease was prepared by reacting an aromatic diisocyanate
(diphenylmethane diisocyante) with a predermined amount of amines
(cyclohexylamine, stearylamine, p-toluidine) in a base oil and diluted
the resultant with a base oil to attain the worked penetration of 280.
Additives are added to this grease to prepare grease compositions of
Examples 1 to 4 and Comparative Examples 1 to 4.

Content of cyclohexyl group (CH)(%)=[{(the number of moles of cyclohexyl
group)/(the number of moles of cyclohexyl group+the number of moles of
alkyl groups)}×100]

[0036] Outer race rotating test which estimates the bearing life under a
high temperature was conducted. The bearing was driven under the
following conditions, and the bearing life was determined when the motor
overcurrent or abnormal vibration was detected, or the temperature of the
motor exceeded the prescribed temperature by +15° C.

[0037] Bearing type: 6203 rubber seal

[0038] Test temperature: 160° C.

[0039] Rotation rate: 16000 rpm

[0040] Test load: radial load 800 N

Bearing Lubrication Life Test (based on ASTM D3336)

[0041] Inner race rotating test which estimates the bearing life under a
high temperature was conducted. The bearing was driven under the
following conditions, and the bearing life was judged when the motor
overcurrent was detected, or the temperature of the motor exceeded the
prescribed temperature by +15° C.

[0051] All of the results of the outer race rotating test and the bearing
lubrication life test of the grease compositions of the Examples 1 to 4
were more than 500 hours, in which compositions the content of the
thickener represented by the general formula (I) in which thickener the
content of cyclohexyl group (CH) was 60 to 95%, and the content of the
ester synthetic oil in the base oil was not less than 20% by mass based
on the total base oil. Therefore, the grease compositions are excellent
in the heat-resistant property and the inflow property.

[0052] In contrast, all of the results of the outer ring rotating test,
the bearing lubrication life test or both of the tests of the grease
composition of the Comparative Example 1 in which the thickener
represented by the general formula (I) in which thickener the content of
cyclohexyl group (CH) is 50%, the composition of the Comparative Example
2 in which the content of ester synthetic oil in the base oil is 10% by
mass based on the total base oil and the composition of the Comparative
Examples 3 and 4 in which the thickener represented by the general
formula (I) in which thickener cyclohexyl group (CH) is not contained is
used is less than 500 hours. Therefore, this shows that the object of the
present invention is not attained.